The present invention relates to a method for producing a thermoplastic filter material, which has been heated for lying in folds and to an apparatus used therefor.
A filter material produced with the known method is known from German Utility Model 93 19 372. In the known filter material, cover layers are folded together with the filter material proper for ensuring that the folds are kept open also under pressure load by the medium flowing there through, i.e. that the folds do not collapse, whereby the passage resistance would be increased. Furthermore, the folds are held together by a cover layer which extends over the backs of the folds. However, during further processing, for instance for obtaining filter inserts, it is difficult to keep the folds of the filter material in such a close vicinity as is required for the filter material shown in FIG. 1 of said utility model.
Thus it is the object of the present invention to provide a method of producing a folded filter material in which the folds are fixed in a constructional simple manner in close vicinity to each other.
The object is achieved by a method and apparatus in which the thermoplastic filter material which has been heated for forming the folds is accumulated in a cooling path such that said folds are pushed together and fixed by cooling with respect to their shape.
On the one hand, the spaces that are created by the thickness of the folding tools are eliminated between the folds thanks to the measure that the folds are pushed together following the heating operation and the laying in folds. On the other hand, these folds are fixed by cooling, so that it becomes much easier to pass the folds in a densely packed state to or through subsequent steps of the method.
Advantageous developments of the method according to the invention can be gathered from the following description: